The present invention relates to a plasma processing device, and in particular to a plasma processing device using a cathodic arc discharge.
In recent years, study of a thin film deposition technique using a low pressure arc discharge has been vigorously conducted. In such a technique, an arc discharge is generated by bringing an electrode generally called striker in mechanical contact with a target portion serving as a cathode or by using an electron beam to let an arc current of several tens amperes flow into the target portion. Plasma is sustained by making ions from plasma hump generated in an upper space of the target collide with the cathode and thereby generating ions and electrons from the cathode. Plasma including these ions and electrons is efficiently led to a vacuum reaction chamber by using a magnetic field duct for transportation and a magnetic field duct for scanning. The plasma is thus applied uniformly to a substrate to be processed. Thereby, processing such as thin film forming or etching is conducted.
When plasma is generated by an arc discharge in the above described conventional method, however, a large number of neutral particles having no electric charge or electrically charged particles are generated besides ions and electrons. These hamper the processing such as thin film forming or etching as particles, resulting in a great problem.
As a method for solving the above described problem, using a shape having at least one curvatures in a portion of the magnetic field duct or providing a ring-shaped trap mechanism inversely tapered in the travel direction of plasma generated in an internal wall portion of the magnetic field duct is disclosed in PCT/GB96/00389 Publication.
However, the following facts have been revealed by experiments of the present inventors. The above described technique brings about an effect in removal of neutral particles each having such a particle as to be observed easily by an optical microscope. However, the above described conventional technique extremely decreases the probability that neutral particles each having a particle diameter of at most 5 xcexcm which occupy a greater part of generated particles are trapped on the inner wall of a magnetic field filter. Therefore, removal of such neutral particles each having a particle diameter of at most 5 xcexcm is difficult. Furthermore, as for electrically charged particles each having a particle diameter of at most 5 xcexcm, capture of them is difficult. It is thus necessary to find a new solution at the time of putting thin film formation and etching to practical use.
An object of the present invention is to provide a plasma processing device capable of removing mainly the above described particles each having a particle diameter of at most approximately 5 xcexcm effectively.
In accordance with the present invention, particles included in plasma generated by an arc discharge are broadly classified into electrically charged particles and neutral particles, and an effective capture-removal method is proposed for each of them.
First of all, in order to remove the electrical charged particles each having a particle diameter of at most approximately 5 xcexcm included in plasma, it is necessary to cause the plasma to be passed through at least one electric field filter supplied with a voltage, when leading the generated plasma to a processing chamber, in which a substrate to be processed is held, by using a first, magnetic field duct for plasma transportation and a second, magnetic field duct for applying the plasma uniformly onto the substrate to be processed.
To be concrete, it becomes possible to capture electrically charged particles included in the plasma efficiently in real time by setting a bias voltage applied to an electric field filter to a range of 10 V to 90 V as compared with an installation voltage. This utilizes the fact that each of electrically charged particles floating in the plasma has a negative potential. The reason is believed that it is covered with approximately several thousands electrons.
On the other hand, in order to efficiently capture and remove in real time the neutral particles flying out from the cathode target as a result of an arc discharge, a neutral filter having at least one penetration hole is disposed so as to be nearly perpendicular to the travel direction of the plasma, in a plasma transportation course between the first magnetic field duct and the substrate to be processed. The plasma transported through the first magnetic field duct is made to pass through this neutral filter.
At this time, the sum total of sectional areas of the penetration holes is made to be less than approximately 40% of the sectional area of the first magnetic field duct or the second magnetic field duct.
Furthermore, by covering a part of the surface of the above described neutral filter with an organic macromolecule material or a composite material including it, it becomes possible to prevent exfoliation of neutral particles stuck to the surface of the neutral filter and drastically decrease generation of secondary particles caused by the exfoliation of neutral particles.